In the internal combustion engine of which fuel is injected directly into the cylinder, when the engine is operated with smaller loads, for example, air-fuel mixture burns by being locally formed near a ignition plug (the combustion is so-called a stratified combustion). Such combustion can reduce fuel consumption and purify the exhaust gas.
In the direct injection type internal combustion engine, a multiple ignition system which generates two or more ignitions per one stroke of the engine, and a multi-point ignition system which uses two or more ignition plugs per one cylinder have been proposed to prevent misfire and improve stability of the combustion. For example, Japanese Application Patent Laid-Open Publication No. 2000-179377 discloses such a multiple ignition system.
The multiple ignition system is equipped with an apparatus for measuring the air-fuel ratio comprising a photoelectric transfer element which is provided near the ignition plug. The ignition system ensures the combustion stability by generating a plurality of ignitions from preset ideal ignition timing to maximum retardation ignition timing while controlling the air-fuel ratio by the feedback control. The multi-point ignition system is disclosed by Japanese Application Patent Laid-Open Publication No. 2000-179441.
Combustion stability can be ensured by measuring the air-fuel ratio near the ignition plug and controlling the air-fuel ratio by feedback control. However, such combustion stability is ensured only when the fuel spray is formed locally near the ignition plug. The combustion stability of the whole inside of the cylinder is not always ensured depending upon the fuel spray characteristics of the injection valve, because most of fuel sprays with characteristics of general conical spray (which is formed in the shape of non-hollow or hollow) do not always go towards the ignition plug. Moreover once ignition per one stroke may not be enough to make a complete combustion even if the ignition is performed between the preset ideal ignition timing and the maximum retardation ignition timing, because fluctuation in the air-fuel ratio distribution is great during this period.
Therefore, the conventional system has ensured the combustion stability by generating multiple ignitions, for example, 4 to 5 ignitions, but this method quickens abrasion of the ignition plug electrode and increases power consumption. Furthermore fuel consumption and exhaust gas may not fully be reduced, since the air-fuel mixture is not always enough stratified. In addition, the ignition timing needs correction since the system is affected by deterioration of the engine with the passage of time. Accordingly the system changes the ignition timing intentionally, and takes the data of the ignition timing in connection with the conditions of the engine at that time, and corrects the ignition timing corrects based on the data. As a result, the system is complicated, and the cost becomes high.
This kind of spark type engine has a catalyst in the exhaust pipe to purity the exhaust gas. The catalyst does not function unless its temperature becomes high.
So it is expected to reduce the quantity of exhaust gas by making stable stratified combustions with less fuel until the engine is warmed up after the startup, and to activate the catalyst as early as possible by sending the hot exhaust gas to the exhaust pipe by retarding the ignition timing. For this purpose, there is a method to retard the fuel injection timing. However, when the fuel injection timing is retarded, the pressure in the combustion chamber becomes higher than the conventional spray penetration force and prevents the fuel spray from reaching the ignition plug. This makes the fuel combustion unstable.
An object of the invention is to provide the direct injection type internal combustion engine which can reduce abrasion of electrodes of the ignition plug and consumption of electric power by the simple mechanism while ensuring stable combustion.
Another object of the invention is to provide the direct injection type internal combustion engine which can activate catalyst as early as possible just after the startup of the engine and make the combustion stable by retarding the ignition timing.